Power steering mechanism



United States Patent O v 3,170,535 POWER STEERING MECHANISM David W. Barton, Birmingham, and John R. Elwell, Dearv born, Mich., assignors to Ford Motor Company, -Dearborn, Mich., a corporation of Delaware Y Continuation of application Ser. No. 824,814, July 3, 1959. This application Feb. 23, 1962, Ser. No. 176,488

9 Claims. (Cl. Imi-79.2)

This invention relates generally to power steering mechanisms for motor vehicles, and more particularly to an improved servo Valve for use in such a system.

This application is a continuation of co-pending application S.N. 824,814, filed July 3, 1959, for a Power Steering Mechanism, now abandoned.

Servo valves for use in power steering systems normally include a pair of relatively moveablevalve elements shifta-ble to control application of power, and resilient means for centering the valve'elements when nosteering effort-is being applied. It is important that the valve elements be .accurately centered and their relative movement be uniformly opposed. The resilient centering means utilized by the prior art have often been complex and susceptible to breakage and misadjustment in service. Further, many yof the Vcentering devices in such valves utilize separate resilient elements to resist movement inropposite directions. Thus, any variation in the separate resilient means are manifested in an undesirable difference in feel when steering in different directions. I

It is, therefore, an object `of this invention yto provide lice relative to the arcuately extending slot 26. It will be noted that relative rotation of shafts 10 and 12 will be limited by engagement of pin '28 with the ends of `slot 26.

The periphery ofoutput shaft 12 is grooved at 32 to provide a seat for agenerally cylindrical, axially-split band spring 34. Theband `spring 34 is so proportioned that in the unstressed condition its opposed end faces 36 and 3S have a chordal `separation which is less than the chordal thickness of abutment 30. Further, when the band spring 34 is mounted on the output shaft 12 and its end faces 36 land 38 are in contact with the abutment 30, the inside diameter of the band 1spring is slightly greater than the diameter of the groove 32, thus providing a l centering preload, but smaller than the outside diameter an improved, rugged, and precise servo valve for a motor vehicle power steering gear,

Another object is toprovide a servo valve which gives identical feel in both directions of operation.

An additional object-is to provide such a s ervo valve which employs simple, low-cost parts.. l

Further objects and `advantages of the present invention will be apparent from the following description, reference being had tothe accompanying drawing wherein a preferred form of the present, invention is cle-arly shown.

rInlthe drawing: v The single figure is a perspective view, partly in section, of a servo Valve employing the presentinvention.

.n The preferred form ofthe invention illustrated includes an input shaft 10 which has a spline 11 for connection to the steering wheel 13 of a motor vehicle.

.45 On shaft f 10 ,an output shaft 12 is journalled for rotationV relative l thereto.y The input shaft 10 extends through the hollow output shaft 12 and has an enlarged cylindrical end 14 which concentrically receives one end ofl a valve spool 16. Spool 16 is-a conventional 4-way valve spool which will be slidablyreceived in avalve bore of a conventional valve body, not shown, to regulate interconnection between a pair of motorports 17 and 19 and a pump 15 and a reservoir 21.V The enlarged cylindrical end 14 of input sha-ft -10 includes a longitudinal slot 18- through which a pin 20jixedto 'valve spool 16extends into a helical slot 22 in the output shaft 12.

A spur gear 24 encircles the periphery of output shaft 12 and is. fixed thereto. Gear 24 will engagea rack or other toothed member, schematically indicated at Z3, which connects through the usual steering linkage with a dirigible wheel 25 of the Vehicle. A uid motor 27 is also It will be seen that when no torque is being applied Y to input shaft 10, the band spring 34 willangularly center the shafts 10 and 12 by urging the pin 28 into angular alignment with the -anchor 30. Since the chordal thicknesses of pin 28 and anchor 30 are the same, the two shafts will have an accurately located centered position to which they are continually biased by the band spring 34. It should also be noted that since the band spring 34 in the unstressed condition is so proportioned as to position the faces 36 and 38 closer together than the thickness of abutment 3ii, the shafts 10 and 12 are preloaded to the centered position. v I

v In operation, when a torque i-s applied to the input shaft 10, and the resistance to turning encountered by the output shaft 12 exceeds the preload of band spring 34, the band spring 34 will expand, and the resulting relative rotation between shafts 1G and 12 actuates the valve spool 16 in a longtudinal direction due to the co-action of axial slot 18 and helical slot 22 on the pin 20. It will be noted that regardless ofthe direction of the rotation of shaft 10 the resistance to rotation relative to shaft 12 will be the same, since identical distortion-of the single resilient means 34 will result.` n

It will be seen from the foregoing that there has been provided a simple, rugged, and low-cost servo valve for use in a .power steering mechanism, in which the initial, n

perceptible resistance to actuation will be identical regardless of the direction of the operation.

While the form of embodiment of the invention as herein disclosed constitutes ya preferred form, it is to be understood that other forms might be adopted, all coming within the scope of the claims which follow.V

What is claimed isas follows:

` 1.A A control means for controlling the power means of a power steering mechanism comprising: a driving means; a sensing means.r having concentric telescopically related inputl and *outputy shafts, said input shaftpadapted to be driven by said driving means, a generally cylindrical, axially-splitrband spring encircling the outer of said shafts so as to contract thereon, and presenting opposed ends in spaced relationship, a radially extending arm xed tothe inner of said shafts and extending through an opening in "the outer of said shaftsy located so as to be interposed between said opposed ends of said spring, an abutment member carried by the outer of said shafts longitudinally located with respect to said shafts so as to be interposed between said opposed ends of said spring, and having substantially the same chordal thickness as said arm, said input shaft adapted vtobe rotated relative to said output shaft against the force of said axially-split band spring when the torque applied to said driving means exceeds a selected value, a movable valve element and actuating means movable in response to relative rotation of said shafts of said sensing means and adapted to move the movable valve element, whereby the relative rotation of said input andoutput shafts-causes said valve actuating Y 3, means to actuate said movable valve element to control the power means of powersteering mechanism.

2. VThe structure defined by claim l wherein said split bandiv spring is so proportioned that in the unstressedcondition `vthe chordal distance'between said opposed ends is less'than the chordal thickness of said abutment member. i

3. The structure defined byclaim 1 wherein said opening in the outer of said shafts-is of limited arcuate extent s'o as to limit relative rotation of'said shafts.

4. The structure dened byclaim 1 wherein said valve actuating means comprises a radial slot infone of said shafts, a helical slot in the other of said shafts, and a radially` extending valve actuating member engaging both of-said slots. t

5. A power steering system for a vehicle comprising: an input shaft, a steering wheel connected to' said input shaft, an output shaft, a steerable road wheel, linkage means coupling said steerable road wheel with Ysaid output shaft, a fluid motor connected to said steerable road wheel through said linkage means, a source of fluid under pressure, valve means for controlling the actuation of said iluid motor, said yvalve means being positioned between vsaidsource of `fluid underpressure and said iluid'motor,

cooperating meanson said input and output shaft and on said valve means forractuating said valve means upon relative rotation of said input shaft and said output shaft,

a unitary resilientmember in the form of a (Ii-,spring inter.

connectingr said output shaft vand said input shaft, said C-springpreventing relative rotation between said input shaft and' said output Vshaft when the torque applied to Said input shaft through said steering wheel is 'below' a selected level and expandingtopermitrelative'rotation between said :input shaft and saidoutput shaftwhen the torque applied to said input shaft by said steering wheelexceeds said selectedlevel, `whereby said valve meansl is l actuated and fluidfunder pressure is supplied to saidgiiuid motor when the torque appliedto said input shaft through said steering wheel exceeds said selected level. n k

6..' power steering system-for a vehicle comprising: 'a steering means, aY steerabley element which resists being st'eerableV element, a power moving `means connected to said steerable element, said power moving means only being actuatedk when the force exerted by said steering means is above a givenvvalue, a control means for sensing when the force exertedfby said steering means is above t moved, said steering jmeans operatively coupled to 'said i said given -value and -for actuating the power moving Y means when said given value.is-sensed,vsaid control means connected to said steering means and-said power moving l means, saidcontrol means including a sensing means havspringA encircling said outer shaft so as to contract thereon and presenting opposed'ends-in spacedV relationship; a radially extending arm fixed to saidinner shaft `and extending'through an opening in said outer shaft, located Yso as to be interposed vbetween the ends `of said spring, an abutment member carried by said outer shaft, saidabutment member located withrespiect to said shafts Vso as to 'be interposed between said opposed ends of said spring, said innershaft adapted to rotate Vrelative to said louter shaft when the Yfvorceexerted byjsaid steeringmeans is above said given value; `and valve actuating meansmovable in response to v`thev'relative` rotation'of saidzshafts and adapted to actuate said power moving means sothatsaid power moving means will move'said steeraibleelement;

9. A power steering systeme'for a vehiclek comprising: a steering means, astecrable element which resistsfbeing moved, a power moving means connected to said steerafble 'n element, said -power moving'means only .being actuated Whenthe force 'exerted'byf-said steering means is'abovea selected level,-a control means afor'ysensing when thevforce exerted by said steering meansis abovesaidl selected level and for actua-ting said power movingmeans when said lselected level is sensed, saidcontrol means comprising:

concentric, telescopically related input Vand output shafts,

one lof said. shafts Ybeing an inner' shaft 'and onelof Asaid Y shafts being yan-outer shaft, V,said outer shaftglbeing con-l nected to said steerablemeans, said inner shaft connected to `said steering means, said inner shaftconnectcd-to said outer shaftfto rotate relative jtofsaid outer shaft `when the force exerted by lsaid steering ymeans-is above said selected level,y said connection comprisingi -a` cylindrical axiallysplit 4band-spring,- -said band spring encircling said outer shaft so as to contract thereon and presenting opposedV ends in spacedrelationship,faradially extending armlxed.

to said inner shaft and Vextending Vthrough, anfopeningin said outer sha-ft, ylocated sofas to -be` interposed between.

said opposed ends ofjsaid Lspiing, an a-butimentfmember carried by said outer shaft, longitudinally locatedk with respect to said shaft so as to be Vinterposedbetween said ing a unitary resilient. member having a gap 4whichvis exi pandedV when saidforce exerted by said steering means is s above said given value,-th'e expandingof said gap Vof said resilient member causingl a signalwhereby the control means actuatesthe power moving means.

7. The structure deiined by claim 1,6 wherein said sensing,

means comprises: a firstY shaft operatively coupled to said `steer'able element andhaving an abutment means contacting said unitary resilient mem-ber, a second shaft operaabutment Ymeans on said second shaft tending to exert a vforce to expand the gap of said unitary resilient member n tively coupled to said steering means and having an abut- -ment means contacting said unitary vresilient member,`said opposed endsof AsaidA springs, said abutment member and saidradial arm cooperating ASto.. compress said axially;split .I band spring when the-force exerted by said steering means v isa-bove saidselected level, thereby enabling said inner and outershafts tofrot'aterelative to each other,-and valve means movablein responseto the relative motion of said shafts-and adapted t actuate said powenrmoving `meansso thatsaid power moving means will move* said steerable element; q l Y, Y 4 p p l References-Cited'inthefle of'ithis patent 1 UNITED STATES viparleursl 

1. A CONTROL MEANS FOR CONTROLLING THE POWER MEANS FOR A POWER STEERING MECHANISM COMPRISING: A DRIVING MEANS; A SENSING MEANS HAVING CONCENTRIC TELESCOPICALLY RELATED INPUT AND OUTPUT SHAFTS, SAID INPUT SHAFT ADAPTED TO BE DRIVEN BY SAID DRIVING MEANS, A GENERALLY CYLINDRICAL, AXIALLY-SPLIT BAND SPRING ENCIRCLING THE OUTER OF SAID SHAFTS SO AS TO CONTRACT THEREON, AND PRESENTING OPPOSED ENDS IN SPACED RELATIONSHIP, A RADIALLY EXTENDING ARM FIXED TO THE INNER OF SAID SHAFTS AND EXTENDING THROUGH AN OPENING IN THE OUTER OF SAID SHAFTS LOCATED SO AS TO BE INTERPOSED BETWEEN SAID OPPOSED ENDS OF SAID SPRING, AN ABUTMENT MEMBER CARRIED BY THE OUTER OF SAID SHAFTS LONGITUDINALLY LOCATED WITH RESPECT TO SAID SHAFTS SO AS TO BE INTERPOSED BETWEEN SAID OPPOSED ENDS OF SAID SPRING, AND HAVING SUBSTANTIALLY THE SAME CHORDAL THICKNESS AS SAID ARM, SAID INPUT SHAFT ADAPTED TO BE ROTATED RELATIVE TO SAID OUTPUT SHAFT AGAINST THE FORCE OF SAID AXIALLY-SPLIT BAND SPRING WHEN THE TORQUE APPLIED TO SAID DRIVING MEANS EXCEEDS A SELECTED VALUE, A MOVABLE VALVE ELEMENT AND ACTUATING MEANS MOVABLE IN RESPONSE TO RELATIVE ROTATION OF SAID SHAFTS OF SAID SENSING MEANS AND ADAPTED TO MOVE THE MOVABLE VALVE ELEMENT, WHEREBY THE RELATIVE ROTATION OF SAID INPUT AND OUTPUT SHAFTS CAUSES SAID VALVE ACTUATING MEANS TO ACTUATE SAID MOVABLE VALVE ELEMENT TO CONTROL THE POWER MEANS OF A POWER STEERING MECHANISM. 